Automatic volume control device



May 7, 1957 c. BEvooRT ET AL 2,791,743

AUTOMATIC VOLUME CONTROL DEVICE 3 Sheets-Sheet 1 Filed oct. 1o. 195o SS @Eg-SSE* .w

` INVENTORS: Erie/w ,e/oof/ @d AIH Ml? 7 1957 c. aEvooRT ET Ax. 2,791,743

AUTOMATIC VOLUME CONTROL. DEVICE 3 Sheets-Shea?, 2

O .if l! S E3 W R Nm www @MAI Filed Oct. 10, 1950 INVENTORS: @2726/5249 5e/0017( 5/ az'mozza//ozzafa//afzazza/e May 7, 1957 c. BEvooR'r ET AL 2,791,743

AUTOMATIC VOLUME CONTROL DEVICE 3 Sheets-Shea?l 3 Filed 001'.. 10, 1950 United States Patent O AUTOMATIC VOLUME CONTROL DEVICE Cornelis Bevoort and Raimond Edouard Marie Baudet, The Hague, Netherlands, assignors to Staatsbedrijf der Posterijen, Telegrafe en Telefonie, The Hague, Netherlands Application October 10, 1950, Serial No. 189,412

Claims priority, application Netherlands October 11, 1949 2.1 Claims. (Cl. 323-66) The present invention relates to an automatic volume control device for use in radio termination apparatus and especially for use in the novel termination apparatus set forth in `our copending U. S. application, Serial No. 189,411 which was tiled October 10, 1950. A further copending application tiled in the matter of the novel automatic volume regulator by the present inventors is identified by Serial No. 228,374 which was tiled May 26, 1951, now Patent No. 2,675,328.

In the transmission of speech over a connection, as for example over telephone lines and radio links, the speech level of the several parties utilizing such equipment will vary over an extremely large range, and accordingly it is normally necessary to provide a compensating device for effecting a fairly constant volume or `speech level output. Such equipment is desirably of an automatic nature in that the manual adjustment of such type equipment requires the services of highly skilled technical operators, and even then, because of the monotonous n'ature of the work, the results are quite often unsatisfactory.

The automatic volume regulator equipment of the present invention is arranged for connection in a line section with further channel control equipment, and is operative to automatically adjust the level of the speech being transmitted thereover to a predetermined value, the equipment being operative in the case of a person with a weak voice to decrease the attenuation in the line and thereby provide increased amplification of the speech to the given desired level prior to transmission thereof over the connecting link. With the impression of speech currents of a higher level, as for example, by aparty having a strong, piercing voice, the regulator is operated to increase the attenuation in the line section and thereby decrease the level of the speech to the given desired norm prior to transmission over the connecting link. v

While equipment for effecting automatic volume adjustment has been previously developed, such equipment has normally been somewhat complicated in its arrangement and more expensive to manufacture. Further the speed of operation of the equipment and the reliability thereof in its operation were not always entirely satisfactory.

There is a need for a simplified, more economical type automatic volume control unit, and it is an object of the present invention to provide such improved type of equipment.

The provision of extremely tine control ofthe speech level is largely dependent upon the ability of the equipment to obtain an accurate and true picture of the speech level in this section, and to provide same to the controlling members of the automatic volume regulator. Failing the provision of a true picture, the adjustment accomplished must likewise necessarily be inferior.

It is an especial object of the present invention to provide a novel arrangement which includes an improved type level meter for providing a more true and accurate picture of the speech level conditions in the channel to the automatic regulator apparatus,

Patented May 7, 1957 A feature of the level control device is the manner in which electronic equipment is used to control motor regulating equipment which through a mechanical linkage drives an associated attenuation switch member. In this manner variations occasioned by condenser discharge as normally experienced in electronic devices are avoided. Moreover the novel level control device is not influenced by line faults, line land other noises; is not sensitive to sounds deriving from the receiver; and is sensitive to sudden strong noises which are rapidly limited, the remaining amplitude peaks which might cause overmodulation being cut oif by a further limiter in the arrangement.

A further `feature of the invention is the novel peak level meter which is connected in the input side of -the automatic volume regulator, and which is peak sensitive so as to render the automatic volume regulator eifective only with the presence of incoming speech current in the channel, whereby undesired and unnecessary operation of the automatic volume regulator is prevented.

A further feature of the invention i-s the manner in which the attenuation adjustment is effected more quickly in the event of speech current of a larger than normal value than in the case when the speech current level is below the given normal value.

Other features and advantages of the new and novel automatic volume regulator equipment will become apparent with reference to the accompanying specification and drawings in which Figure 1 illustrates in schematic block form the novel automatic volume regulator as connected in a line terminating arrangement; t

Figure 2 illustrates in detail the automatic volumeregulator of the invention; and

Figure 3 is a graphic illustration of a particular set of current values provided by the level meter in controlling the maximum-minimum relays of the automatic vvolume regulating equipment shown in Figures l and 2.

With reference to Figure l, the channel terminating apparatus there shown comprises an operators position 51 which is connectedrto an incoming channel land an outgoing channel 2 by meansy of a balance transformer S2 and an artificial balancing line 53. The outgoing channel 2 terminates at a transmitter V4 of a given radio link, the speech currents provided by the operator at 51 being conducted over theqoutgoing channel Zto the transmitter 4 for transmission thereby 'to an associated receiver (not shown) at the other end of the radiolink. The incoming channel 1 includes a radio receiver 3`which is associated with the transmitter (not shown) at the other'end of the link (which is similar to the illustrated transmitter 4) and which is operative to receive the incoming radio-frequency signals and transmit correspond ing audible-frequency signal currents over channel 1 to the operators position 51.

The outgoing channel includes an automatic volume regulator unitv 54, an amplifier 19, an attenuation path 16, a irst channel enabling switch 13, apsecond channel enabling switch 12, a peak-limiter unit 9, an attenuation path 8, and an 'amplifier 6, the output thereof being con- 'nected tothe modulator stage of the transmitter 4.

The incoming channel extending between the radio receiver 3 and the operators positionY 51 comprises an amplier unit 5, a noise limiter unit 7, rst and second :channel enabling switches 10 and 11, an attenuation path 17 and an amplifier 18. The channels may further include key members 14 and 15 for inserting secret speak-v ing device 20 in the equipment as desired, the privacy unit being of a type described pending application.

A diiferential commutator 55 arranged to be controlled by speech currents occurring in the incoming and outgoing channels is intercon-nected across the channels 1 and 2, and is operative at its' output side to control in the aforementioned co.

one of the two channels 1 land 2 to conduct speech thereover as is more fully described inthe copending application and hereinafter.

Switching relays 44 and 45 control the operation of units 10, 11, 12 and 13, the units being operative to conduct current thereover when the centers of the coil diagonals are connected and being operative to interrupt current transmission when the center coil connection is broken.

Switch control unit 46 which controls the privacy installation 20 is operatively controlled in series with switches 44 and 45 by the differential commutator 55.

In operation, the channel terminating apparatus effects enablernent of the alternative channels as required to provide the desired communication link, maintains the signal level as supplied to the transmitter within a given range, suppresses random noises which may be present in the link prior to amplification in the channel apparatus, and effects the establishment of a communication link in which singing and other echo phenomena are eliminated. The terminating apparatus is further operative to provide preference for one of the channels, the incoming channel in the present embodiment being rendered normally conductive and bei-ng suppressed when speech occurs in the outgoing channel.

Briey, as speech currents are produced by a party at the operators equipment 51, the speech currents are applied to the outgoing channel 2 over the balance transformer 52 to the automatic volume control unit 54, which is operative to regulate the volume of the speech current passing through the channel and to maintain same between predetermined limits. In the embodiment illustrated herein, the equipment is operative to adjust the variable attentuation network associated with the volume control to elect a decrease in the speech current level as soon as the input speech current surpasses the value of 16.5 db.

Alternatively the automatic volume control unit 54 operates to decrease the attenuation in the channel, and thereby effect an increase in the level of the speech current, whenever the speech level descends below a given minimum value which in this embodiment is 34.5 db.

Such limits have proven successful in an operative embodiment in which the mean level on the two-wire path is approximately -24 db on the two-wire side, and in which the level varies between a maximum of and a minimum of -35 db, the termination attentuation being 5 db.

Speech currents at the output side of the automatic volume control unit 54 are extended over an amplier 19, attenuation network 16, switches 13, and 12 (assuming there is no speech in the incoming channel), peak-limiter 9, which is connected in the outgoing channel 2 for the purpose of preventing overmodulation of the transmitter by instantaneous speech currents for which the automatic volume control unit 54 cannot readily compensate, attenuation path 8, and amplifier 6V to the modulating stage of the transmitter unit 4 for transmission over the radio link.

Signals incoming to the channel terminating apparatus from the other end of the radio link are received by a radio receiver unit 3 and extended over a receiver ampliiier unit 5, a noise suppressor unit 7 (which prevents response of the equipment to random noises), the enabled switches 10, 11 and 14 (assuming priority 'prefence for the speech currents on incoming channels), attenuation path 17, amplifier 18, and the balance transformer 52 to the operators position 51. The noise suppressor 7 is operatively controlled in accordance with the presence or absence of incoming speech currents to apply equal or diferent direct current voltages to associated equipment, the attenuation'of'the circuit being reduced about 2O db by such apparatus whenever speech is received. It is assumed in the use of equipment adjusted to these values that the incoming speech currents are at least 10 db stronger than the noise level. The noise suppressor 7 is also adjusted to be preferably sensitive to frequencies appearing in the speech band whereby the differential commutator is substantially protected against false operation by transient line disturbances.

Differential commutator 5S is connected between incoming channel 1 and outgoing channel 2, and is sensitive to speech currents as they appear in either of these channels to control associated switching equipment such as relays 44, 45 to alternatively enable the corresponding one of the incoming or outgoing channels.

The disablement of one :channel and the enablement of the other is accomplished in the time of several milliseconds whereby the possibility of the presence of singing and echo phenomena is substantially eliminated. The switches 44, 45 in the positions shown in Figure l effect enablement of the incoming channel 1 and disablement of outgoing channel 2. The arrangement is adjusted so that with impression of speech currents on the incoming path with speech on the outgoing channel, the transition time appears to be in the order of 3 milliseconds; with speech on the incoming channel and the impression of speech currents on the outgoing channel, the transition time appears to be about S0 milliseconds.

A more detailed explanation of the operation of the differential'commutator 55, and other termination equipent appears in our aforementioned copending application, and in an application for Automatic Volume Regulators which was filed May 26, 1951 and received Serial No. 228,394. The specic operation of the novel automatic volume regulator of the invention and the features thereof are now set forth in detail.

Automatic volume control unit 54 The strength of the speech currents as applied by a party over the interconnecting two-wire members to the operators equipment V51 and the hybrid balance transformer 52 normally varies over a fairly large range of values, the signals being frequently outside the preferred operating range of a modulating stage of a conventional transmitter such as illustrated at 4. The automatic Volume control unit is automatically operative to adjust the'speech level variations as fed to the channel `2, whereby the signals applied to the modulating stage of the transmitter 4 are of the strength for which optimum operating results are obtained.

Automatic volume regulator 54 basically comprises a first level meter 58 whichis arranged to control a zero or control relay 60, and a second level meter 59 which is arranged to control a series relay arrangement including a maximum relay 62 and a minimum relay 64. Zero relay 60, maximum relay 62, and minimum relay 64 control associated contacts 61, 63 and 65, respectively, which contacts are connected in a circuit arrangement for controlling'an energizing circuit to a motor panel 71 which controls operation of a regulating motor 72.

Motor unit 72 in turn controls associated shaft means 77 to adjust a variable attenuation network 56 to various positions to vary the value of attenuation inserted in the outgoing channel 2. Thus the speech level in the channel as modified by the automatic volume regulator 54 is always within given predetermined limits.

Level meter 58 isa peak sensitive meter which controls a Zero relay to condition the automatic volume regulator 54 for operation with the presence of speech on the input path 66. Level meter 59'is connected to the channel on the output side of the automatic volume regulator and is operative to supply currents indicative of the level fof the speech currents in the channel to the motor controlling relays 62 amd64. The level meters together control the three relays 60, 62 and 64 to energize the motor 72 in such manner that the attenuation network S6 maintains a constant speech level in' the channel.

Level meter 58 Level meter 58 measures the input level of the speech currents to the automatic volume regulator 54 and condition same for operation with the detection thereby of the presence of speech currents in the channel.

The level meter 58 is preferably sensitive only to fre quencies between 300 and 3000 kc. with a peak at the central frequencies whereby the operation of the automatic volume regulator equipment S4 responsive to transient noise disturbances is substantially minimized.

Level meter 58 basically comprises a vacuum control tube 100, which is normally biased to conduct, and which in its operation between its conductive and nonconductive conditions is operative to elect energizati'on and deenergization of an associated zero relay 60.

In the absence of speech currents in the channel the control tube 100 is normally conductive, relay 6,0 is normally energized, and contacts 61 associated therewith are lopen to prevent operation of the auto-matic volume regulator apparatus 54. As speech currents above a predetermined level appear in the channel, control tube 100 is biased to cut-olf and the energizing circuit for zero relay 60 is interrupted. Relay 60 restores, and contact 61 associated therewith is operative to extend the operating potential on conductor 68 to the contacts of the maximum and minimum relays 62 and 64 respectively to condition the automatic volume regulator 54 for operation.

In more detail level meter 58 as shown in Figure 2, comprisesa by-pass filter 97 connected to the outgoing channel 2 which detects the signals thereon, and transmits them to the primary side of an input transformer 98. The secondary of the input transformer 98 is connected to the input side of a rectifier bridge 99, the output of the bridge 99 being connected over a filter network comprised of units 101-105 inclusive to the gridcathode circuit of control tube 100. That is, one side of thel output of rectiiier bridge 99 is connected to the parallelly connected resistance 102 and rectifier 101, which is in turn connected to resistance 103. The other output conductor of the rectifier network 99 is connected to a first and second capacitor set 104, a switch member 105 being alternatively adjustable to each of two positions to include one of the capacitors in the circuit as desired. It is apparent therefrom that the rectier 101 and the RC network comprising resistances 102, 103 and the selected one of the capacitors 104 are operative to extend the output signals of rectifier-bridge 99 to the grid-cathode circuit of the tube 100.

Control tube 100 as illustrated in Figure 2, comprises a pentode tube including a plate or anode, a suppressor grid, a screen grid, a control grid, and a cathode. The suppressor grid is connected to the cathode circuit in the conventional manner, and the screen grid is connected over a resistance 106 to a power supply having a positive potential somewhat lower in value than the potential applied to the plate of the tube. Resistance 106 is an adjustable resistance so that the potential applied to the screen grid may be varied to provide different level responding characteristics for the level meter as desired.

The plate circuit of tube 100 is connected to a source of positive supply, over the winding of the zero relay 60.

The cathode of tube 100 is connected to ground in the conventional manner.

In operation with the presence of speech currents in channel Z, the bandpass filter 97 and transformer 98 effect the application of corresponding speech signals on the input path for rectier network 99 of the peak level meter 58, which network rectiiies the signals and extends them over the network 101-105 to the control grid of normally conductive tube 100. As the value of the speech current surpasses a predetermined level, `the incoming signals applied to control grid oftube 100 are strong enough to overcome the biasing voltage therefor, whereby the conductivity of tube 100 is 'reduced to 'effect the restoration fof the zero relay 60. Relay 60 'restores and at its contacts 61 extends the operating potential on conductor 68 to the contacts of the maximum-minimum relays 62 and 64 respectively. The automatic voltage regulator 54 is now conditioned for operation.

The peak level meter 58 operates so as to render the control relay 60 slow-to-release, and quick to operate. That is, as outgoing speech currents appear at the peak level meter input 58, current flows through capacitor 104 from left to right, over switch 105, resistance 103, and the network comprised of rectifier 101 and high value resistance 102 to the bridge 99. A positive charge is thus placed on the left hand plate of capacitor 104 and a negative voltage is placed on its right hand plate. Since resistance 102 is a high value resistance, the RC product is large, and the capacitor is charged slowly, whereby the tube assumes the nonconductive state with some delay. As the tube lis rendered nonconductive after the elapse of a predetermined period of time determined by the RC component of the circuit, relay 60 restores.

With the disappearance of outgoing speech at the input side of the peak level meter 58, capacitor 104 begins to dischargeover a circuit which extends over rectifier bridge 99,` rectifier 101, and resistance 103. Since the rectifier'101 is conductive in this direction, the high resistance 102 is bypassed and the capacitor 104 discharges quickly over resistance 103. Control tube 100 is thereby quickly rendered conductive, and relay 60 is rapidly operated as a result of the disappearance of speech on the channel. Rectifier circuit 99 is, of course, of a value which does not restrict the discharge of capacitor 104.

' Relay 60 is made quick to operate so that with interruption of the outgoing speech in the channel, contact 61 will open before contact 65 (controlled by the minimum relay of level meter 59) closes to initiate a futile adjustment of regulator 56. Likewise, with the occurrence of speech in the outgoing channel, level meter 59 must have the opportunity to respond before contacts 61 are closed, so that only the desired adjustments will be effected once the set is energized by closure of contacts 61.

Y In one embodiment the peak level meter was adjusted to effect 'cutoff of control tube 100 and the consequent conditioning of the automatic volume control regulator 54 whenever the speech currents were stronger than -40 db. In such arrangement relay 60 was constructed to operate with provision of a 4 ma. current.

Lever meter 59 Lever meter 59 is connected to respond to the speech current output of attenuation pad 56 as amplified approximately 20 db by amplifier 57, and is operative to provide a mean level signal which is accurately indicative of the value of the speech currents in the channel.

The level meter basically comprises a pair of pentode control tubes 90, 91 interconnected to provide a mean level signal over a rectifier network 93 to eiect control of the maximum-minimum relays 62, 64 respectively. Thus the level meter 59 is operative to supply at a certain mean input level, a corresponding direct current for controlling operation of the maximum-minimum relays 62 and 64. With operation of the maximum relay 62, operating potential is extended over conductor '70 to the panel 71, whereby attenuation pad 56 is adjusted to insert increased attenuation in the channel. With the decrease of the mean level input beneath a given value the minimum relay 64 releases to extend operating potential over conductor 69 to panel 71, whereby the attenuation in the outgoing channel is reduced.

In more detail, the level meter 59 is connected to the channel by a resistance pair 78 and an input transformer 79. The lever meter pentode control tubes and 91 each comprise a plate, a suppressor grid, a screen grid,

a control grid and a cathode. The secondary of the input transformer 79 is connected to the grid-cathode circuit of the first tube 90.- The plate circuit of tube 90 is connected to a suitable plate potential energizing source over resistances S and 84, and is further connected over a network comprising capacitor 85' and resistanccs 86, 87, to the grid-cathode circuit of control tube 91.

The suppressor grid of tube 90 is connected in conventional manner to the cathode circuit, and the screen grid thereof is connected over capacitor 83 to the cathode circuit and over resistance 82 to the plate circuit. The cathode of tube 90 is connected over resistances 7S and 94 to ground.

Control tube 91 which is controlled by tube 90 has its plate connected to the positive potential source which also supplies the plate of control tube 90. The suppressor grid of control tube 91 is connected to the cathode circuit in a conventional manner, and the screen grid is connected to the plate circuit for tubes 90 and 91.

As before mentioned, the control grid for tube 91 is coupled to the plate circuit of control tube 90. The cathode of control tube 91 is connected over resistance 92 to ground.

The plate circuit of control tube 91 is coupled to a ectier network 93, one side of the input circuit for the rectifier being connected over capacitor 89 and inductance 8S to the grid plate circuit of tube 91 and over its other side to resistance 94 and ground. The second input connection also extends over resistance 75 to the cathode circuit of the first control tube 90 to provide a negative feed back circuit for effecting liner control.

Maximum and minimum relays 62 and 64 are connected in series to the output side of the rectifier network 93 and are bridged by capacitor 95. Resistance 96 is connected intermediate the maximum and minimum relays, and one of the conductors in the output circuit of the rectilier network 93.

In operation, the output voltage of attenuator 57 is applied over resistances 73 to the primary of input transformer 79, which extends the signals over the secondary of the transformer to the control grid and cathode of control tube 90.

Application of the various signals to the control grid of tube 9i! effects corresponding variations of the voltage which appears in the plate circuit of tube 90, which varia tions are applied to the grid cathode circuit of tube 91. The corresponding vvariations appearing in the plate circuit of tube 91 are transmitted to the rectier network 93 over the inductive coupling circuit, which transmits a proportional D. C. signal to the maximum-minimum relays 62 and 64 respectively. A negative feed back path extending from the rectifier network 93 across resistance 75 to the cathode of the first amplifier tube insures provision of a more constant operating amplifier unit. Capacitor 95 operates as a smoothing capacitor for the two relays 62 and 64 and prevents fluttering thereof.

The windings of the maximum relays 62 and minimum relay 64, as well as the shunt resistance 96 across the maximum relay, are chosen so that in the operating range both the relays 62 and 64 are excited by an equal number of ampere turns.

With an average input level, a corresponding direct current is applied by rectifier network 93 which is of a value to energize minimum relay 64. With decrease of thc input level a predetermined amount below the average value, the output current drops and the minimum relay 64 will release to etiect application of operating potential over conductor 69 to the motor panel. As the speech current level on path 57 approaches the maximum limit,V

the output of level meter 59 increases to the point that the maximum relay 62 is operated and operating potential is extended over conductor 70 to the motor panel.

With reference to Figure 3, there is shown thereat in graphic form the relation between the input level of the transmission measuring set and the relay currents, as well as the adjusting limits for a dynamic range of 15 db.

Assuming the mean level on the two wire side is 20 db, andthat it varies between maximum 0 and minimum -35 db, the termination attenuation being 3.5 db, and that the attenuation path 56 has a 45 db range'7 amplitier 57 supplies 18.5V db amplification. At the mean level (-20 db) of the two wire path, and pad 56 on -20 db, the level of -20 db-3.5 db-2O db-i-l8.5 db=25 db, will appear at the level meter 59. Minimum relay 64 will remain energized in such instance, and maximum relay 62 will remain deenergized and accordingly no operating potential will be extended to the motor panel.

Assuming speech dynamics at -15 db and starting from no speech condition, the minimum relay 64 will have to operate at the current corresponding to the minimum limit, and the maximum relay will have to, excite at a current corresponding to a value 2 db above the maximum limit.

At diminishing level, starting from a very high level, the maximum relay will release at the maximum limit and the minimum relay will release at a point 2 db below the minimum limit.

Assuming the starting limits in this example as -119 db, the minimum limit will be -34 db, this being the minimum value at which the current variation is still large enough to operate a relay. Inasmuch as the motor normally regulates 45 db in seven seconds, Vit is possible that overmodulation might occur with the sudden appearance of the high level for a very brief interval. It is therefore desirable to more rapidly reverse the motor, that is 45 db in one second such as by reduction of the field. Overmodulation could then only be produced during part of this second for sudden level increase. Smoothing capacitor connected across thc relays 62 and 64 prevents relay oscillation with syllables in the speech.

Level meter 59 should be independent of frequency variations. Accordingly the controller shaft may carry a second variable resistor in phase with Vthe controller and enabling the position of the controller to be supervised by a meter on a control table.

Motor panel 71 Control of motor 72 and the mechanically coupled attenuation pad 56 is effected by the application of operating potential alternatively to input conductors 69 or 70. With application of potential to conductor 69 as a result of too low a level at the input side of the automatic volume regulator 54, the motor is operated to reduce the attenuation supplied by pad 56; with the application of operating potential to conductor 70 as a result of too high a level at the input side of the automatic volume regulator 54, the motor is operated in the opposite direction to increase the attenuation suppliedby attenuator 56.

In order to avoid distortion, overload of amplifiers etc., as a result of too high an input level, the reducing of the high levels is effected as quickly as possible and in such instances -a resistor is connected in series with the field winding of the motor to provide a weaker ield and increased speed of rotation of the motor.

The motor panel 71 basically comprises a control switch 125, a iirst relay 197, a motor energizing circuit controlled thereby to effect the operation of the motor 72 at a predetermined rate of speed in one direction, a second relay 112 operative to complete a motor energizing circuit to operate same in the reverse direction at a rate of speed dilierent than said rst rate, minimum and maximum limit contact switches 74 and 73, a cam 76, and a pad controlling shaft 77 which is driven by motor 72a, supervisory relay 122, pilot lamps 119, and 121, and alarm 124.

The panel 71 is prepared for automatic operation by closure of switch to the position illustrated in Figure 2, which switch at its contacts 125:1, 125b prepares the energizing circuits for motor control relays 107, 112 rearnhem spectively and at its contacts 125c`energizes a pilot lamp 121 to inform the attendant of its prepared condition.

Operation of the motor 73 to adjust attenuation pad 56 to increase or decrease the attenuation in the outgoing channel '2 is accomplished with the alternativeV impression of a potential on panel input conductors 69`and 70 respectively by the level meter 59. That is, as the speech current output of the automatic volume regulator 54 approaches the maximum limitthe, output current of level meter 59 rises to a point which effects operation of maximum relay 62 which in its operation is effective at its contacts63 to apply potential to conductor 70 which extends over contacts 1256, the winding of relay 112, contacts 163, the minimum limit switch contacts 74,v to negative battery. Relay 112 operates and at its contacts 113 interrupts a point in the energizing circuit for relay 107 to prevent simultaneous operation thereof; at its contacts 114, 116, 117 completes an operating circuit for the motor 72, which circuit extends from negative battery over contacts 117, 116,` motor 72 and conta-cts 114 to ground; and at its contacts 115 inserts a resistance 118 in the field winding 72A of motor 72. Motor 72 operates in a :counterclockwise direction to effect adjustment of the shaft means 77 to increase the value of attenuation inserted in the channel by'attenuation pad 56, and thereby decrease the speech level output of the automatic volume regulator 54.

Similarly when the speech level input tothe levelmeter 59 decreases below a minimum value, the minimum relay 64 restores and at its contacts 65- effects the extension of positive potential on conductor 68 over contacts 61, 65, conductor 69, contacts 125:1, relay 107, contacts 113 and maximum limit switch contacts 73 to negative battery.

Relay 167 operates and at its contacts 108 interrupts the energizing circuit for the motor control relay 112 to prevent the possibility of operation thereby for the period that relay 107 is operated; at its contacts 109, 110 and 111 completes an operating circuit for motor 72, which extends from negative battery over contacts 111, contacts 110, motor 72, and contacts 109 to ground.

Motor 72 now operates in clockwise direction (at a slower speed than before) to drive shaft means 77 to decrease the attenuation inserted in the channel by pad 56.

It is apparent that with adjustment of the level-ineither direction, as the speech level is brought into the yacceptable limits, the output of level meter 59 will be such as to operate minimum relay 64 and release maximum relay 62, whereby energization of the motor 72 is terminated.

Minimum and maximum position limit stop 'contacts 74 and 73 respectively are mounted adjacent the cam 76 on shaft 77 for operation thereby to establish given limits of adjustment for the shaft member 77, contact members 74 and 73 being mounted so as to terminate motor operation as the shaft reaches the two extreme positions which correspond to the minimum and maximum attenuation which can be provided by the variable attenua-tion network 56. n

Suitable signal means such as pilot lamps 119, 120 are connected to a potential source in series with the contacts and are illuminated to inform-the attendant whenever the equipment is operated to a limiting position. Relay 122 may be included with the pilot lamps in the supervisory circuit in such manneras to operate an associated audible alarm such as 124. l

It is apparent that with movement of switch 125 to its central position, the potential impressed upon conductors 69 and 70 by level meter 59 will be without effect, and selective manual control may be provided in an obvious manner.

Conclusion There has been set forth hereinbefore, an automatic volume regulator unit including a motor control arrangement which utilizes a minimum amount of equipment m 10 eecting a maximum degree of control in an extremely rapid and reliable manner. As a result a more constant volume output isachieved fora given variable input.

The attenuator in the regulator which varies lthe attenuation in the channel, and consequently the level of the speech therein, is adapted to be operated by a directly connected electrical motor which is operable in either of two directions at different speeds, the motor being operative at one speed in one direction to increase the attenuation inserted by the associated attenuator, and operative in the other directionat a second speed to decrease the attenuation inserted in thechannel. The motor controlling circuit includes a minimum number of elements, andis in turn controlled'by only three supervisory relays. As a result speedier operation is achieved, and closer control is obtained. v

Two of the supervisory relays are controlled by a novel level meter which providesan extremely accurate picture of the'mean level of the speech currents in the channel. The 'third relay is controlled by another novel level-meter of similar operating characteristics.

Individually novel features in the level meters of the equipment, such as the negative feed back circuit which is connected between the rectifier and amplifier equipment of the level meter, insures a more constant type control. Smoothing apparatus at various points in the apparatus further aid in the elimination of spurious responses to syllabic inputs.

The inherently simple arrangement of the minimum amount of elements insures provision of an arrangement which responds more quickly and more reliably to provide a more constant volume control, and is believed to be a definite step forward in the art.

While the invention has been illustrated and described ina given embodiment, nevertheless it will be understood that such is merely exemplary, and in that numerous modifications and rearrangements may be made therein without departing from the scope of the invention.

What is claimed is:

. 1. An automatic volume control unit for use in a line section comprising in combination: attenuating means operative to various predetermined positions to vary the speech level in said section, a first level meter including a first switching means operative to condition said attenuating means for operation Aonly in response to impression of speech frequencies of a predetermined value and upon the input side of said unit and operative to disable said attenuating means responsive to reduction of the level of the incoming speech below avpredetermined valueya second level meter connected in the output side of said attenuating means comprising means for providng a control current in yaccordance with the mean level of said speech current in said section, a second and third switching means connected to `the output side of said second level meter and operative responsive to said mean level output of said second level meter being of a'value less than a predetermined minimum and of a value in excess a predetermined maximum value respectively, a motor for operating said attenuating means to its various positions having two directions of rotation; motor control means for operating the motor at different velocities of rotation in different directions, and contact means controlled only by said first, second and third switching means for operating said motor control means to maintain the output of said unit at a predetermined mean value.

2. An automatic volume control unit as set forth in claim 1 in which said first switching means includes relay means operative to apply a' control voltage to the contacts of said second and third switching means only responsive to the appearance of speech currents at a predetermined level at the input side of said volume control unit;

' 3. An automatic volume control unit as set forth in claim 1 in which said second and third switching means 'A l l are connected in series in the outputicircuit ofvsaid second level meter, and which includes a resistance connected in shunt across .said third switching means for determining the operating characteristics thereof relative to the desired range of operation for the volume control unit.

4. An automatic volume control unit as set forth in claim l in which said motor controlling means comprise a first relay having contact means for controlling said motor to rotate in a rst given direction at a first given speed, and a second relay having contact means for effecting rotation of said motor in an opposite direction at a second rate of speed, and guard contacts controlled by said first and second relay interconnected to effect interruption of the energizing circuit for the opposite relay with self energizaton, whereby simultaneous excitation of the first and second relays is prevented.

5. An automatic volume control unit as set forth in claim l including limit means for preventing adjustment of said attenuator means past predetermined maximum and predetermined minimum positions, and alarm means operative with adjustment of said attenuator means to either of said two limit positions.

6. An automatic volume control unit for use in a line section comprising in combination: attenuating means operative to various predetermined positions to vary the speech level output of said volume control unit, a first level meter including means for rendering it sensitive only to speech frequencies impressed on the input side of said unit, a rst switching means control led thereby operative to disable said attenuating means responsive to reduction of the level of the incoming speech below a predetermined value, a second level meter connected in the output side of said unit comprising level'control means for providing a control current proportional to the mean level of the speech current in said channel, said level control means comprising an input transformer, a first and second electronic tube member each comprising at least an anode, a grid and a cathode element, means for connecting the output side of said transformer tothe grid cathode circuit for said first tube, resistor coupling means for conducting the voltage variations of said first tube to said second tube to control the effective operation thereof, a rectifier circuit, coupling means for connecting the output of said second tube to said rectifier circuit, and a constant volume feedback circuit connected between said first tube and said rectifier whereby a mean level output of more constant value is provided at the output side of said rectifier, a motor for operating said attenuating means to its various positions having two directions of rotation and two velocities ofy operation, and a second and third switching means connected to the output side lof said rectifier for operatively controlling said motor responsive to a signal of a value which is less than a predetermined minimum and a signal which is greater than a predetermined maximum value respectively.

7. An automatic volume control unit as set forth in claim 6 in which said second and third switching members are connected in series in the output side of said rectifier e u l1 circuit and which includes a smoothing capacitor connected across said series relay arrangement.

8. in an automatic volume regulator, Ia peak-level meter for use in controlling operation of the automatic volume regulator in accordance with the presence and absence of speech in a given channel comprising' transformer means having a primary and secondary winding, means for connecting the primary of said transformer-to said channel, a rectifier bridge having an input circuit connected to the secondary winding of said transformer, a control tube including atleast an anode, a control grid and a cathode, potential biasing means for normally biasing said tube to be conductive, and an RC circuit for connecting the output of said rectifier bridge to said con trol grid of said tube to bias said tube to cutoff responsive to the presence of speech in said channel,` a relay conv12 necte'd to be operatively controlled by said control tube, and volume regulator means operatively controlled by said relay in its operation to adjust the speech level in said channel. Y

9. A peak-level meter as set forth in claim 8 in which said RC circuit provides a signal of a value sufficient to overcome the normal tube biasing potential to bias said tube to cutoff with the presence of speech currents of a predetermined value on said channel and thereby effect operation of said relay to adjust said volume regulator means.

l0. A peak-level meter as set forth in claim 8 in which said RC circuit includes a plurality of capacitors and a switching means for effecting insertion of alternative ones of said capacitors in said RC circuit, and in which the value of said potential biasing means for said control tube is adjustable.

11. In a mean level meter for use in an automatic volume regulator in providing a direct current signal proportional to the value of speech currents in a given channel, a first and second electronic tube member, each of said tubes comprising at least an anode, a grid and a cathode element, an input transformer having a primary and secondary winding, means for connecting the primary winding of said input transformer to said channel to detect the variable speech level thereon, means for connecting the secondary winding output of said transformer to the grid-cathode circuit of said Afirst tube member, resistor coupling means for conducting the voltage variations which appear in the plate of said first tube member as effected by the variable speech current to the grid-cathode circuit |of said second tube member, a rectifier bridge circuit, coupling means for connecting the output of said second tube member to said rectifier bridge, and an output circuit for said rectier bridge over which a direct current signal indicative of the speech level in the channel is provided.

12. In a Imean level meter for use in an automatic volume regulator for providing a direct current signal pro portional to the value of the speech currents in a given channel, a first and second electronic tube member, each of which comprises at least an anode, a grid and a cathode element, an input transformer having a primary and secondary winding, means for connecting the primary winding of said input transformer to said channel, means for connecting the secondary winding of said transformer to the grid-cathode circuit of said first tube member, resistor coupling means for conducting the voltage variations as effected on the plate of said first tubev member to the grid cathode circuit of said second tube member, a rectifier bridge circuit, Vcoupling means for connecting the output of said second tube member to said rectifier bridge, and a constant volume feed .back circuit'connected between the cathode circuit of said first tube member and said rectifier bridge to provide a'direct current output signal of amore constant mean level output.

.1.3. An arrangement as set forthin claim `1 which includes switch means operative .to a first position to con nect said first, second and third switching means for control by said motor control means, and alternatively to av second position to connect saidmotor control means for manual operation.

14. An arrangement as set forth in claim 8 in which said RC circuit includes a high resistance member, and in which said peak level meter includes meansV for rendering said high resistance effective inr 'the RC circuit with the appearance of speech in said channel and for rendering same ineffective with the Ydisappearance of speech in said channel.

15. An arrangement as set forth in claim Vtl in which said peak level meter includes means for effecting cut-off of said control tube in a first given period of time, and for rendering said control Vtube conductive in a substantially shorter time period. A

16. ln an automatic volume regulator, a mean level meter for use in controlling the level of speech in an associated channel, including a rst means for introducing attenuation into the channel and a second means for decreasing the attenuation in the channel, and a peak level meter including control means operative to control the energization circuits for said irst and second means in said mean level meter, and timing means for controlling said control means to become effective at a first rate responsive to the appearance of speech in said channel and at a second rate responsive to the disappearance of speech in said channel.

17. In an automatic volume regulator, volume control means for controlling the level of speech in an associated channel, means for detecting the speech conditions in the channel including a control tube member; control means for controlling conductivity of said tube member including an RC circuit for varying the operating periods for said control means, said RC circuit including a high resistance member, and means for rendering said high resistance member effective in said RC circuit with the appearance of speech in said channel to delay the operation of the tube member, and operative with the disappearance of speech in said channel to reduce the etectiveness of the resistance member to thereby accelerate operation of the tube member; and means controlled by said tube member for operatively controlling said volume control means.

18. In an automatic volume regulator, means for controlling the level of speech in an associated channel including a mean level meter means comprising means operative to provide a control signal which is proportional to the mean level of the speech current output from said channel, attenuation means for said channel attenuation control means including, a iirst means for controlling same to increase the attenuation in the channel, a second means for controlling same to decrease the attenuation in the channel, means operative to simultaneously apply said control signal to said iirst and second means to control sarne in maintaining the level of speech in said channel within a predetermined range, and a peak level meter means including means operative to enable said first and second means to operate said attenuation means only responsive to the occurrence of speech signals in the channel.

19. An automatic volume control unit for use in controlling the speech level in a line section comprising in combination: attenuating means operative to various predetermined positions to vary the speech level output of said volume control unit, a rst level meter means connected to the input side `of said unit operative to enable and disable said attenuating means responsive to the presence and absence of speech of a predetermined level in said section, a second level meter means connected to the output side of said unit comprising a mean level meter means operative to provide a control signal proportional to the mean level of the speech current in said channel, means in said mean level meter means including a potential storage device 'operative to minimize the control eected by peak voltages which occur in the control signal responsive to the receipt of instantaneous peaks in the speech level output, whereby an increased dynamic range is provided for such equipment, and control means controlled by said control signal to adjust said attenuation means to provide the desired speech level output.

20. An automatic voltune control unit :as set forth in claim 1 which includes a iirst speed control means operative to control said motor to operate at a first speed, and a second speed control means operative to control said motor to operate at a second speed which is substantially greater than said rst speed, and circuit control means including said second and said third switching means and said contact means operative to control said motor control means to enable said irst speed control means responsive to the mean level speech being of less than a predetermined value, and to enable the second speed control means responsive to the mean output level surpassing a predetermined maximum value.

2l. An arrangement as set forth in claim 16 in which said timing means includes a signal generating circuit operative to provide a control signal for said control means at a iirst rate responsive to the disappearance of speech in said channel, and a control device in said circuit to control same to provide a second signal at a slower rate than said first rate responsive to the appearance of speech currents therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,811,954 Mitchell et al. June 30, 1931 1,811,955 Mitchell et al June 30, 1931 2,462,551 Renner Feb. 22, 1949 2,462,552 Renner Feb. 22, 1949 2,563,179 Malsbary Aug. 7, 1951 2,617,864 Johnson Nov. 11, 1952 2,631,188 Clapp Mar. 10, 1953 

